Air cooled coaxial magnetron having an improved arrangement of cooling fins

ABSTRACT

An air cooled coaxial magnetron is disclosed. The magnetron includes a coaxial arrangement of anode and cathode electrodes to define a magnetron interaction region in the space therebetween. The anode electrode includes an anode wave circuit and a coaxial circular cavity resonator with a cylindrical common wall disposed therebetween, such wall having an array of axially directed coupling slots communicating between the circular cavity and the wave circuit for controlling the frequency of the tube. An inner heat shunt is affixed to one end of the cylindrical anode wall and extends axially of the tube for connection to a radially directed heat shunt and to an array of radially directed cooling fins. An outer axially directed heat shunt interconnects the outer ends of the cooling fins to the radially directed heat shunt to enhance thermal conduction of heat from the anode wall to the cooling fins for improved cooling efficiency of the tube.

United States Patent [72] Inventor Richard M. Ilynes Westfield, NJ. 211Appl. No. 5,026 [22] Filed Jan. 22, 1970 [45] Patented June I, 1971 [73]Assignee Varian Associates Palo Alto, Calif.

[54] AIR COOLED COAXIAL MAGNE'IRON HAVING AN IMPROVED ARRANGEMENT OFCOOLING FINS 7 Claims, 3 Drawing Figs.

[52] U.S. Cl 315/39.77, SIS/39.75, 313/40, 313/46, 313/36 [51] Int. ClH01j 25/50 [50] Field ofSearch 315/3977, 39.75, 39.51; 313/40, 45, 46

[56] References Cited UNITED STATES PATENTS 3,169,2ll 2/1965 Drexler etal 315/3977 3,383,551 5/1968 Gerard ABSTRACT: An air cooled coaxialmagnetron is disclosed. The magnetron includes a coaxial arrangement ofanode and cathode electrodes to define a magnetron interaction region inthe space therebetween. The anode electrode includes an anode wavecircuit and a coaxial circular cavity resonator with a cylindricalcommon wall disposed therebetween, such wall having an array of axiallydirected coupling slots communicating between the circular cavity andthe wave circuit for controlling the frequency of the tube. An innerheat shunt is affixed to one end of the cylindrical anode wall andextends axially of the tube for connection to a radially directed heatshunt and to an array of radially directed cooling fins. An outeraxially directed heat shunt interconnects the outer ends of the coolingfins to the radially directed heat shunt to enhance thermal conductionof heat from the anode wall to the cooling fins for improved coolingefficiency of the tube.

PATENT El] JUN H911 SHEET 1 [1F 2 AIR S M R m WM WD IR A H m R BY WATTORNEY PATENIEDJUH H371 3582707 SHEET 2 0F -2 INVENTOR.

RICHARD M. HYNES BY gwdbk :1 m

ATTORNEY AIR COOLEI) COAXIAL MAGNETRON HAVING AN IMPROVED ARRANGEMENT OFCOOLING FINS DESCRIPTION OF THE PRIOR ART Heretofore, coaxial magnetrontubes having a cathode coaxially surrounded by an anode wave circuitwhich in turn communicates with an outer surrounding cavity via theinter mediary of an array of coupling slots through the anode wall haveincluded an arrangement of cooling fins carried on the outside wall ofthe cavity resonator for cooling of the tube. Heat generated in themagnetron interaction region and picked up on the cylindrical anode wallwas conducted axially of the tube to the end walls of the cavity andthence via the end wall of the cavity to the outer wall and thence tothe inner ends of the colling fins. In such an arrangement the thermalpath from the anode wall to the cooling fins was relatively long andresulted in relatively poor and inefficient cooling of the anode wall,thereby severely restricting the operating power level of the tube.Moreover, by placing the cooling fins on the outside wall of the cavitythe diameter of the tube was thereby substantially increased tending toincrease the size of the tube.

SUMMARY OF THE PRESENT INVENTION The principal object of the presentinvention is the provision of an improved air cooled coaxial magnetron.

One feature of the present invention is the provision, in an air cooledcoaxial magnetron, of an axially directed inner heat shunt having anarray of cooling fins affixed thereto and extending transversely of thetube together with a transverse heat shunt and an outer axial heat shuntinterconnecting the outer ends of the cooling fins to the outerextremity of the transverse heat shunt for improving the conduction ofthermal energy from the anode wall to the cooling fins and, thus,improving the cooling efficiency of the tube.

Another feature of the present invention is the same as the precedingfeature wherein the cavity resonator is circular and coaxially surroundsthe cylindrical anode wall and wherein the cooling fins are disposedadjacent one end of the cavity in a region nonaxially coextensive withthe cavity, whereby the provision of the cooling fins does notappreciably increase the size of the tube.

Another feature of the present invention is the same as the firstfeature wherein the cylindrical anode wall coaxially surrounds thecircular cavity resonator and the cathode surrounds the anode wall.

Another feature of the present invention is the same as the secondfeature wherein a pair of C-shaped permanent magnets are affixed to thetube and straddle axially the circular cavity resonator and array ofcooling fins for providing an axially directed magnetic field in theinteraction region.

Other features and advantages of the present invention will becomeapparent upon perusal of the following specification taken in connectionwith the accompanying drawing wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an end view of a coaxialmagnetron incorporating features of the present invention,

FIG. 2 is a sectional view, partly in section and partly in elevation,taken along line 2-2 of FIG. I in the direction of the arrows, and

FIG. 3 is a longitudinal view, partly in section, of an alterna tivecoaxial magnetron incorporating features of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. I and 2,there is shown a coaxial magnetron tube I incorporating features of thepresent invention. More specifically, the tube 1 includes'a circularcentral body portion 2 having a cathode insulator and stem assembly 3depending axially from one end thereof and having a tuner assembly 4inwardly extending from the other end thereof. The cathode stem assembly3 supports a thermionic cathode emitter 5 centrally of the tube on theaxis thereof. The other end of the cathode emitter 5 is supported via aninsulator 6 from the body ofthe tube 2.

The main exchanging portion 2 includes a hollow cylindrical anode wall7, as of copper, coaxially surrounding the cathode emitter 5 and havingan array of vane resonators 8 radially inwardly projecting from the wall7 to establish a wave circuit for supporting microwave energy in energyexchanging relation with an electron stream circulating in an annularinteraction region 9 between the inner ends of the vane resonators 8 andthe cathode emitter 5.

A toroid-shaped circular electric mode resonator II is contained withinthe central body portion 2 and surrounds the anode wall 7. The anodewall 7 includes an array of elongated wave energy coupling slots 12providing wave energy communicating passageways between the circularelectric mode resonator II and alternate vane resonators formed by theregion between adjacent vanes 8. An annular electrically conductivetuning plunger 13 is disposed at one end of the circular resonator IIand is axially translatable via tuner actuating rods I4 affixed todiametrically opposed portions of the annular tuning plunger l3 andextending axially of the tube.

A rectangular output waveguide 15 communicates through the outer wall 16of the circular resonator llll via a coupling aperture 17 for couplingwave energy from the tube 1 to a load, not shown, via the intermediaryof an output microwave window 18 sealed across the waveguide 15. Thewindow structure 18 includes an output waveguide flange 19 for couplingthe tube to a similar flange on a waveguide, not shown, incorporated inthe load.

A pair of hollow cylindrical axially directed magnetic pole members 21and 22 are axially spaced apart on opposite sides of the vane resonators8 to define a magnetic gap in the interaction region 9. A pair ofC-shaped permanent magnets 23 and 24 have their ends connected to polemembers 2k and 22 for providing the magnetomotive force to energize themagnetic gap with a strong axially directed DC magnetic field. TheC-shaped magnets are diametrically opposed on the body 2 of the tube andextend outwardly from the tube in spaced quadrature from the position ofthe tuning plungers 14.

A lossy mode absorber ring 25, as of carbon impregnated alumina ceramic,is disposed on the inside of the anode wall 7 adjacent the upper end ofthe coupling slots 12 for absorbing undesired wave energy associatedwith a mode of oscillation in the coupled array of slots 12. Theabsorber ring is brazed to an annular thermally conductivechannel-shaped frame member 26, as of copper, which in turn is brazed toa cylindrical absorber retaining ring 27, as of copper, which is affixedto the anode wall 7 via screws 28. The absorber frame 26 and retainingring 27 serve to facilitate conduction of thermal energy generated inthe absorber 25 from the region of the absorber to the anode wall 7 andthence in the axial direction of the tube. In addition, the absorberretaining ring 27 abuts the outside of the upper pole piece 2I such thatthermal energy generated in the absorber is also conducted via a pathincluding the retaining ring 27 and pole piece 22 in a direction axiallyof the tube.

An inner thermal shunt 29 is formed by a hollow cylindrical section ofthe tube body which is affixed, as by brazing, to the upper end of theanode wall 7 and which abuts the absorber retaining ring 27 and the polepiece 211. Two arrays of cooling fins 31 and 32, respectively, areaffixed as by brazing along their curved inner edges to the outersurface of the inner heat shunt 29. The cooling fins 3i and 32 have atypical thickness of 0.040 inches and are axially spaced by a distance,as of 0.047 inches. The cooling fins 31 and 32 project radiallyoutwardly from the inner thermal shunt 29 on diametrically oppositesides of the tube. Each cooling fin is a curved sector of a flat ringsubtending approximately 130 of arc. At one end the cooling fins 31 and32 are spaced by approximately 25 of arc to accommodate one of thetuning plungers 14. At the other ends of the cooling fins the ends ofthe fins are spaced apart by approximately of arc and are terminatedalong a chord crossing the inner open end of a rectangular air duct 33through which air is directed into the fins from an air blower, notshown.

The outer side edges of the fins are affixed to outer axially directedheat shunts 34 and 35, as of one-eighth inch thick curved copperplate.The inner and outer heat shunts 29, 34 and 35, respectively, areinterconnected at one end via a radially directed heat shunt 36 formedby an annular plate, as of seven-sixteenths inch thick copperplate. Theheat shunts 29, 36 and 34, 35 are brazed together at their joining edgesto provide thermally conductive joints therebetween to facilitate theconduction of thermal energy therethrough.

In operation, heat generated by interception of the electrons on thevanes 8, by transfer of thermal radiation and conduction from thecathode 5, and by absorption of microwave energy in the mode absorber 25is conducted axially of the tube to the axial heat shunt 29 via anodewall 7, retaining ring 27 and via the pole piece 21. Heat is thenconducted from the inner thermal shunt 29 to the fins 31 and 32 andthence to the air stream flowing through the arrays of cooling fins 31and 32 from the duct 33. In addition, some of the thermal energy isconducted radially from the inner heat shunt 29 via the radial heatshunt 36 to the outer heat shunts 34 and 35 and thence to the coolingfins for dissipation of thermal energy in the air stream.

In the absence of the outer thermal shunts 34 and 35, the temperature ofthe fins 31 and 32 would decrease in the radial direction as depicted bydotted line 37 in the plot of temperature versus distance depicted inFIG. 2 above the fin array 31. This reduction in temperature in theradial direction along the fin decreases the efficiency of the fins forcooling of the tube. The provision of the radial shunt 36 and outershunts 34 and 35 provides a second heat path to the outer ends of thefins such that the temperature of the inner and outer ends isapproximately the same to maintain a more uniform temperature over thefins in the radial direction shown by curve 38.

Provision of the cooling fins 31 and 32 in the position indicated inFIG. 2, namely, in axial alignment with and at one end of the cavity 11,substantially improves the cooling efficiency of the tube as contrastedwith a prior art design wherein the fins were placed at the outerperiphery of the cavity 11. More particularly, in the prior art design,100 cubic feet per minute of air flow at a back pressure of 3.5 inchesof water with a temperature rise in the air of 35 C. was required inorder to dissipate approximately 1,100 watts in the tube. In the tube ofthe present invention, 65 cubic feet per minute of air with the sametemperature drop and with a back pressure of only 2.0 inches allowed1,200 watts dissipation in the tube. Moreover, the arrangement ofcooling fins of the present invention substantially reduces thetransverse dimensions of the tube as compared with the prior design.

The air duct 33 includes an arcuate cutout section at 41 to accommodateone of the tuning plungers 14. The tuning plungers 14 are sealed viabellows 42 to the upper end wall of the cavity 11 formed by the radialheat shunt 36. The tuning plungers are moved in the axial direction viaa yoke member 43 connected to the ends of the tuning plungers 14 viascrews 44. The yoke is connected centrally to a screw, not shown, whichis translated in the axial direction by means of a captured nut which,in turn, is turned via a worm screw 45 mating with teeth at the outerperiphery of the nut. An inner bore of the upper magnetic pole piece 21is sealed off by a cylindrical plug 46 which also serves as a bearingmember at its outer surface for the axially translatable tuner screw.

Referring now to F IG. 3, there is shown an alternative tube embodimentutilizing the cooling fin arrangement of the present invention. Moreparticularly, the tube 48 is a reverse coaxial magnetron of the typegenerally described in US. Pat. No. 3,4l4,76l, issued Dec. 3, 1968 andhaving an inner circular cavity resonator 49 surrounded by an array ofoutwardly directed vane resonators 51 which, in turn, are surrounded byan annular cathode emitting ring 52. An array of axially, directedcoupling slots 53 communicate through the outer well of the cylindricalresonator 49 with alternate vane resonators for locking the circularelectric mode of the resonator 49 to the 1r mode of the vane resonatorarray. A mode absorber ring 54 surrounds the upper end of the anode walladjacent the upper end of the slots 53 for absorbing wave energy fromthe slot mode to prevent slot mode oscillations.

A pair of hollow cylindrical magnetic pole members 55 and 56 projecttoward each other along the axis of the tube 48 and are spaced apart attheir inner ends to define an annular magnetic gap through theinteraction region between the vane resonators 51 and the inner surfaceof the cathode emitter 52. The pole pieces 55 and 56, as of iron, aresealed in a vacuum tight manner, as by brazing, to a pair of transverseend walls 57 and 58, respectively, ofa hollow cylindrical main bodyportion 59 of the tube 48.

A high voltage cathode stern assembly 61 projects radially outwardly ofthe tube body 59 and includes a central lead for connection to theannular cathode emitter assembly 52 which is supported from and withinthe main body 59 via a plurality of axially directed standoff insulatorassemblies 62 disposed at a plurality of points located about theperiphery of the cathode emitter 52.

A pair of C-shaped permanent magnets 63 and 64 are fixed at their endsto the pole members 55 and 56 to provide the magnetomotive force for themagnetic gap. Output wave energy is extracted from the resonator 49 viaa circular electric mode waveguide 65 axially aligned with the cavity49. A microwave window 66, as of alumina ceramic, is sealed across thewaveguide for maintaining the vacuum integrity of the tube.

The lower end of the cavity 49 is defined by an annular tuning disc 67,as of copper, which is carried upon an axially directed tuning rod 68for producing axial translation of the tuning disc 67. The upperextremity of the rod 68 is coupled to a transverse crankshaft 69 in atuning structure 71 disposed at the upper end of the tube 48.

The upper end of the circular electric mode cavity 49 is closed off by ahollow cylindrical axially directed inner heat shunt 72, as of copper.An array of radially directed annular cooling fins 73, as of copper, arebrazed at their inner periphery to the outer periphery of the inner heatshunt 72. An annular radial heat shunt 74, as of copper, is brazed tothe outer periphery of the inner heat shunt 72 and extends outwardlyparallel to the fins 73. An outer axial directed curved heat shunt 75,as of copper, is brazed across the outer ends of the fins 73 and to theradial heat shunt 74 to provide a highly thermally conductive path fromthe inner heat shunt 72 via the radial and outer shunts 74 and 75,respectively, to the outer ends of the fins 73 to maintain a relativelyuniform temperature across the radial extent of the fins. The outer heatshunt 75 includes diametrically opposed apertures for mating with acooling air duct, not shown, and an exhaust port for exhausting thecooling air. Thermal energy generated in the anode wall of the circularelectric mode cavity 49 and in the mode absorbing ring 54 is conductedvia the axial inner heat shunt 72 to the fin array 73 and thence to thecooling air to be carried away from the tube 48. A certain fraction ofthe thermal energy will be conducted by the radial shunt 74 to the outerheat shunt 75 and thence to the cooling fins 73 to be dissipated in thecooling air. The mode of operation and the advantages of the inner,radial, and outer heat shunts connected to the cooling fins 73 in thetube of FIG. 3 is substantially the same as the mode of operation andadvantage obtained from the similar arrangement of parts in the tube ofFIGS. 1 and 2.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention can be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What I claim is:

1. in an air cooled magnetron tube, means forming an anode electrodehaving a wave circuit portion for supporting wave energy thereon, meansforming a cathode electrode substantially concentrically disposed ofsaid anode in spaced relation from said anode wave circuit portionthereof to define an annular cross field interaction region in the spacebetween said anode and said cathode electrodes, said anode electrodeincluding a circular cavity resonator dimensioned to support a circularelectric mode of resonance at substantially the operating frequency ofthe tube, said anode also including a generally cylindrical wall portionhaving an array of axially directed coupling slots therethroughproviding wave energy communication between said anode wave circuitportion and said cavity resonator for locking the operating frequency ofthe wave energy on the anode wave circuit to the operating frequency ofsaid cavity resonator, The Improvement Comprising, means forming aninner thermally conductive heat shunt structure connected in thermalconductive relation to one end of said cylindrical anode wall andextending axially of the tube for conducting thermal energy from saidanode wall axially of the tube, means forming an array of relativelythin closely spaced thermally conductive cooling fins affixed at oneedge to said inner heat shunt and extending radially outwardlytherefrom, said fins being disposed with the plane of said finsgenerally transverse to the longitudinal axis of the tube, means forminga thermally conductive radially directed heat shunt connected to saidinner heat shunt and extending radially outwardly therefrom, and meansforming a thermally conductive outer axially directed heat shuntinterconnecting the outer ends of said cooling fins and said radial heatshunt for enhancing thermal conduction from said anode wall to saidcooling fins for improved cooling efficiency of the tube.

2. The apparatus of claim 1 wherein said inner heat shunt meanscomprises a generally tubular metallic structure coaxially disposed ofsaid cylindrical anode wall and affixed at one end to one end of saidcylindrical anode wall.

3. The apparatus of claim 1 including tuning means disposed at one endof said circular cavity resonator for axial translation within saidcavity for tuning thereof, and a pair of tuner actuating rods affixed tosaid tuner means at opposed positions and extending axially of the tubein a region axially coextensive with both said inner thermal shunt andsaid fin means.

4. The apparatus of claim 3 including a pair of C-shaped permanentmagnet members each affixed at both ends to the tube apparatus anddisposed straddling said cavity and said cooling fins for providing anaxially directed DC magnetic field in said crossed field interactionregion.

5. The apparatus of claim 1 wherein said inner, outer, and radial heatshunts are made of copper, and said cooling fins are made of copper.

6. The apparatus of claim 1 wherein said cavity resonator coaxiallysurrounds said cylindrical anode wall, and said array of cooling finsand said radial heat shunt are disposed adjacent one end of said cavityin a region nonaxially coextensive with said cavity.

7. The apparatus of claim 1 wherein said cylindrical anode wallcoaxially surrounds said circular cavity resonator.

1. In an air cooled magnetron tube, means forming an anode electrodehaving a wave circuit portion for supporting wave energy thereon, meansforming a cathode electrode substantially concentrically disposed ofsaid anode in spaced relation from said anode wave circuit portionthereof to define an annular cross field interaction region in the spacebetween said anode and said cathode electrodes, said anode electrodeincluding a circular cavity resonator dimensioned to support a circularelectric mode of resonance at substantially the operating frequency ofthe tube, said anode also including a generally cylindrical wall portionhaving an array of axially directed coupling slots therethroughproviding wave energy communication between said anode wave circuitportion and said cavity resonator for locking the operating frequency ofthe wave energy on the anode wave circuit to the operating frequency ofsaid cavity resonator, The Improvement Comprising, means forming aninner thermally conductive heat shunt structure connected in thermalconductive relation to one end of said cylindrical anode wall andextending axially of the tube for conducting thermal energy from saidanode wall axially of the tube, means forming an array of relativelythin closely spaced thermally conductive cooling fins affixed at oneedge to said inner heat shunt and extending radially outwardlytherefrom, said fins being disposed with the plane of said finsgenerally transverse to the longitudinal axis of the tube, means forminga thermally conductive radially directed heat shunt connected to saidinner heat shunt and extending radially outwardly therefrom, and meansforming a thermally conductive outer axially directed heat shuntinterconnecting the outer ends of said cooling fins and said radial heatshunt for enhancing thermal conduction from said anode wall to saidcooling fins for improved cooling efficIency of the tube.
 2. Theapparatus of claim 1 wherein said inner heat shunt means comprises agenerally tubular metallic structure coaxially disposed of saidcylindrical anode wall and affixed at one end to one end of saidcylindrical anode wall.
 3. The apparatus of claim 1 including tuningmeans disposed at one end of said circular cavity resonator for axialtranslation within said cavity for tuning thereof, and a pair of tuneractuating rods affixed to said tuner means at opposed positions andextending axially of the tube in a region axially coextensive with bothsaid inner thermal shunt and said fin means.
 4. The apparatus of claim 3including a pair of C-shaped permanent magnet members each affixed atboth ends to the tube apparatus and disposed straddling said cavity andsaid cooling fins for providing an axially directed DC magnetic field insaid crossed field interaction region.
 5. The apparatus of claim 1wherein said inner, outer, and radial heat shunts are made of copper,and said cooling fins are made of copper.
 6. The apparatus of claim 1wherein said cavity resonator coaxially surrounds said cylindrical anodewall, and said array of cooling fins and said radial heat shunt aredisposed adjacent one end of said cavity in a region nonaxiallycoextensive with said cavity.
 7. The apparatus of claim 1 wherein saidcylindrical anode wall coaxially surrounds said circular cavityresonator.